1. Field of the Invention
The invention relates to a component for use in wavelength division multiplexing applications, more particularly to a wavelength division multiplexed (WDM) coupler and to a method for making the same.
2. Description of the Related Art
Referring to FIG. 1, a conventional WDM coupler disclosed in U.S. Pat. No. 6,185,347 is shown to include a WDM filter 1, first and second gradient-index (GRIN) lenses 2, 3, a dual fiber pigtail 4, and a single fiber pigtail 5. During manufacture, the first and second GRIN lenses 2, 3 and the WDM filter 1 are first fixed together by applying a heat-curing epoxy 6. Then, after adjusting the relative positions of the first GRIN lens 2 and the dual fiber pigtail 4 to obtain a lowest possible reflection loss for the dual fiber pigtail 4, the dual fiber pigtail 4 is fixed to the first GRIN lens 2 by applying a heat-curing epoxy 601. Subsequently, after adjusting the relative positions of the second GRIN lens 3 and the single fiber pigtail 5 to obtain a lowest possible insertion loss for the single fiber pigtail 5, the single fiber pigtail 5 is fixed to the second GRIN lens 3 by applying a heat-curing epoxy 602.
In the aforesaid conventional WDM coupler, the heat-curing epoxies 6, 601, 602 require a relatively long curing time. Hence, the heat-curing epoxies 6, 601, 602 are likely to spread over confronting end surfaces of the first and second GRIN lenses 2, 3 and the WDM filter 1, confronting end surfaces of the first GRIN lens 2 and the dual fiber pigtail 4, and confronting end surfaces of the second GRIN lens 3 and the single fiber pigtail 5 during the epoxy curing process, which can lead to inferior optical signal transmission.
Referring to FIG. 2, another conventional WDM coupler is shown to include an inner metal tube 7 formed with three sets of weld holes 701, 702, 703. An optical filter unit 8, a dual fiber collimator 9, and a single fiber collimator 101 are mounted in the inner metal tube 7. The optical filter unit 8 includes a ring 801 and a filter component 802. The dual fiber collimator 9 includes a first GRIN lens 901, a dual fiber pigtail 902, a glass tube 903, and a collimator tube 904. The single fiber collimator 101 includes a second GRIN lens 102, a single fiber pigtail 103, a glass tube 104, and a collimator tube 105. The inner metal tube 7 is disposed in an outer metal tube 106. During manufacture, the filter component 802 is bonded adhesively to the ring 801 to form the optical filter unit 8, and the optical filter unit 8 is inserted into the inner metal tube 7 such that the ring 801 is registered with the weld holes 701 in the inner metal tube 7. The weld holes 701 are then filled with solder material to fix the optical filter unit 8 in the inner metal tube 7. To prepare the dual fiber collimator 9, the first GRIN lens 901 and the dual fiber pigtail 902 are inserted into the glass tube 903 and, after adjusting the relative positions of the first GRIN lens 901 and the dual fiber pigtail 902 to obtain a lowest possible reflection loss for the dual fiber collimator 9, the first GRIN lens 901 and the dual fiber pigtail 902 are fixed in the glass tube 903 with the use of an adhesive. Thereafter, the glass tube 903 is fixed in the collimator tube 904 with the use of an adhesive. The dual fiber collimator 9 thus prepared is inserted into the inner metal tube 7 such that the collimator tube 904 is registered with the weld holes 702 in the inner metal tube 7, and the weld holes 702 are filled with solder material to fix the dual fiber collimator 9 in the inner metal tube 7. To prepare the single fiber collimator 101, the second GRIN lens 102 and the single fiber pigtail 103 are inserted into the glass tube 104 and, after adjusting the relative positions of the second GRIN lens 102 and the single fiber pigtail 103 for beam alignment, the second GRIN lens 102 and the single fiber pigtail 103 are fixed in the glass tube 104 with the use of an adhesive. Thereafter, the glass tube 104 is fixed in the collimator tube 105 with the use of an adhesive. The single fiber collimator 101 thus prepared is inserted into the inner metal tube 7 such that the collimator tube 105 is registered with the weld holes 703 in the inner metal tube 7 and such that the single fiber collimator 101 is disposed in the inner metal tube 7 at a position corresponding to a lowest possible insertion loss for the single fiber collimator 101, and the weld holes 703 are filled with solder material to fix the single fiber collimator 101 in the inner metal tube 7. Finally, the inner metal tube 7 is inserted into the outer metal tube 106, and the opposite ends of the outer metal tube 106 are sealed.
Some of the drawbacks of the aforementioned conventional WDM coupler, which can be used to join or split optical signals having different wavelengths, are listed as follows:
1. While it is possible for the WDM coupler of FIG. 2 to alleviate the problem of undesired spreading of epoxy over component surfaces that is commonly encountered in the conventional WDM coupler of FIG. 1, numerous additional components are required, such as: the ring 801 for positioning the filter component 802; the glass tubes 903, 104 and the collimator tubes 904, 105 for positioning the first and second GRIN lenses 901, 102 relative to the dual fiber pigtail 902 and the single fiber pigtail 103; and the inner metal tube 7 having the optical filter unit 8, the dual fiber collimator 9 and the single fiber collimator 101 welded thereto. In addition, because the first and second GRIN lenses 901, 102 are separate from the filter component 802, the structure of the conventional WDM coupler of FIG. 2 is not only more complicated, the axial length and radial dimensions of the conventional WDM coupler of FIG. 2 are increased as well, which result in a larger size for the conventional WDM coupler of FIG. 2.
2. In view of the need to fix the optical filter unit 8, the dual fiber collimator 9 and the single fiber collimator 101 separately in the inner metal tube 7, the manufacturing process is not only lengthened, the heat generated when fixing each of the aforesaid components in the inner metal tube 7 can damage the adhesive bonds among the various components, e.g., those among the first GRIN lens 901, the dual fiber pigtail 902 and the glass tube 903 of the dual fiber collimator 9, which can lead to relative movement among the various components and which in turn can affect the quality of optical signal transmission.
3. As described hereinabove, the manufacturing process for the conventional WDM coupler of FIG. 2 requires the optical filter unit 8, the dual fiber collimator 9 and the single fiber collimator 101 to be assembled separately prior to fixing in the inner metal tube 7. The manufacturing process as such is both troublesome and time-consuming.